ROOT CANAL INSTRUMENT

Description

[0001] The present invention relates to a root canal instrument for treating a root canal of a tooth and a method for its manufacture. Furthermore, the use of a nickel-titanium alloy for the manufacture of a root canal instrument is also described.

[0002] Root canal instruments are known from the state of the art, for example from DE 202012012526 U1. Root canal instruments must exhibit a certain degree of flexibility in order to be able to follow the curves and turns of a root canal in order to perform appropriate root canal treatment. For this purpose, root canal instruments have a core, i.e., a solid material core, extending from a working area of ​​the root canal instrument, which continuously widens conically towards a shaft area of ​​the root canal instrument. Molars, in particular, have a relatively complex root canal system, in which the root canal instrument must also follow small radii of the root canal. For this purpose, the working area of ​​the root canal instrument must be even more flexible.This has so far been achieved by further tapering the core of the root canal instrument, which, however, leads to less mechanical stability of the working area and thus carries a certain risk of part of the working area breaking off during root canal treatment.

[0003] EP1 759 656 A1 discloses a root canal instrument comprising a shaft and a working area attached to the shaft, wherein the working area consists of a nickel-titanium alloy.

[0004] US 5 044 947 A discloses a Ni-Ti-Cu alloy for orthodontic wire, an additional element selected from Co, V, Cr, Mn, Fe, Mo, W and Al can be added.

[0005] It is therefore an object of the present invention to provide a dental root canal instrument and a method for its production, which, with a simple yet stable construction and simple, cost-effective manufacture, has improved flexibility and, in particular, can also follow strong turns of a root canal of a tooth.

[0006] This object is achieved by a root canal instrument, a method for its production, and its use having the features of the independent claims. The subclaims describe preferred developments of the invention.

[0007] The dental root canal instrument according to the invention, with the features of claim 1, has the advantage of being characterized by excellent flexibility. This allows the inventive root canal instrument to perfectly follow the curves and turns of the root canal during root canal treatment, even in difficult-to-access molar root canals, without the risk of breaking off the working area of ​​the root canal instrument. Thus, dead or infected pulp tissue can be completely removed from the root canal with a high degree of reliability. This achieves the most comprehensive elimination of microorganisms present in the root canal.

[0008] The root canal instrument comprises a shaft and a working area attached to the shaft, the working area being made of a nickel-titanium alloy comprising 38 to 46 at% nickel, 46 to 53 at% titanium, and 5.5 to 8.8 at% copper. The geometry of the root canal instrument can be designed as usual, i.e. in particular tapered from a first end of the working area, which is connected to the shaft, to a second, exposed end of the working area. The working area serves as a cutting area for the root canal and in particular comprises a plurality of cutting edges arranged along a core. By using a nickel-titanium alloy as defined above, the working area is formed from a highly flexible material which is nevertheless characterized by high mechanical stability, i.e. in particular a high tensile stress of at least 800 MPa, as well as high bending capacity and / orIt is characterized by a high Young's modulus combined with good ductility, effectively preventing breakage during use of the root canal instrument. Due to its physical and mechanical properties, the copper-containing nickel-titanium alloy is ideally suited for creating a highly flexible working area for a root canal instrument.

[0009] According to the invention, to improve the fatigue strength, the nickel-titanium alloy consists of 38 to 46 at% nickel, 46 to 53 at% titanium, 5.5 to 8.8 at% copper and 0.05 to 0.15 at% chromium.

[0010] According to a particularly preferred embodiment, the nickel-titanium alloy consists essentially of 40.5 to 43.1 at% nickel, 48.7 to 50.8 at% titanium, 6.3 to 8.4 at% copper, and 0.08 to 0.13 at% chromium, and in particular of 42.50 at% nickel, 49.90 at% titanium, 7.50 at% copper, and 0.10 at% chromium. "Essentially" means that no other alloying metals or additives are actively added, although small amounts of metals or additives may be present in the form of impurities in the materials used.

[0011] To further stabilize the alloy structure, the nickel-titanium alloy according to ASTM F 2063-15 contains a maximum of 500 ppm oxygen and nitrogen and / or a maximum of 500 ppm carbon and / or a maximum of 50 ppm hydrogen. Specifically, the total oxygen and nitrogen content is below 500 ppm, the carbon content is below 500 ppm, and the hydrogen content is below 50 ppm.

[0012] To improve the bendability of the working area, the nickel-titanium alloy is tempered in a temperature range of 350 to 450 °C. This means that the nickel-titanium alloy forming the working area was heat-treated for a period of approximately 5 minutes to 4 hours in a temperature range of 350 °C to 450 °C, thereby optimizing the lattice structure of the alloy lattice.

[0013] Induction heat treatment lasting from 1 second to 60 seconds at a temperature of 500°C + / - 20°C has also proven advantageous. This can also improve the lattice structure of the alloy.

[0014] Another advantage is that the nickel-titanium alloy was work hardened to 21 to 40% and especially to 35% before mechanical processing (e.g. before machining to form the working area).

[0015] In order to improve not only the bendability but also the mechanical stability with regard to extensibility, thereby counteracting in particular the breakage of the working area under high torsional forces, the nickel-titanium alloy was quenched to room temperature after heat treatment or tempering. For the purposes of the present invention, quenching is understood to mean quenching from the tempering temperature or the heat treatment temperature to room temperature, i.e., to approximately 20 to 25°C. This is achieved in particular by bringing the tempered or heat-treated nickel-titanium alloy into contact with a medium maintained at room temperature. The medium is not specifically limited and can comprise gases, such as nitrogen or carbon dioxide, or liquids, such as water and other inert solvents.

[0016] Quenching in water is particularly advantageous. It has been found that water, due to its high heat capacity, ensures particularly rapid cooling of the nickel-titanium alloy, thereby further improving both the bendability and ductility of the working area.

[0017] Furthermore, the root canal instrument advantageously comprises axially arranged sections with different helix angles, each made of the nickel-titanium alloy. Due to the different geometries of the sections, a working area can be formed that is characterized by a particularly sharply tapered shape toward the second, exposed end. However, due to the use of the nickel-titanium alloy, this working area is characterized by sufficiently high mechanical stability and flexibility without any risk of breakage.

[0018] Furthermore, the invention also describes a method for producing a root canal instrument as disclosed above. In other words, the method according to the invention serves to produce the root canal instrument according to the invention. The method initially comprises a step of providing a nickel-titanium alloy in the form of a strand, wherein the nickel-titanium alloy comprises 38 to 46 at% nickel, 46 to 53 at% titanium, 5.5 to 8.8 at% copper, and 0.05 to 0.15 at% chromium. In a subsequent process step, the strand is processed to form a working area. The processing can comprise any processing method suitable for nickel alloys, and in particular mechanical processing. After completion of the working area, it is connected to a shaft. The shaft is not specifically limited and can, for example,also made of a metallic material or of a plastic.

[0019] The advantages, advantageous effects, and refinements described for the root canal instrument according to the invention also apply to the method according to the invention for manufacturing the root canal instrument. Furthermore, with regard to any definitions, reference is made to the above explanations.

[0020] Advantageously, in light of improving the bendability of the working area, the nickel-titanium alloy is tempered in a temperature range of 350 to 450 °C. As already explained above, the nickel-titanium alloy forming the working area is heat-treated for a period of approximately 5 minutes to 4 hours in a temperature range of 350 to 450 °C, which allows the lattice structure of the alloy to be optimized. Tempering is advantageously carried out in a furnace under an oxygen atmosphere. However, a variant can also include tempering in a vacuum and / or under an argon atmosphere.

[0021] According to an alternative heat treatment, the nickel-titanium alloy is heat-treated by induction for 1 second to 60 seconds at a temperature of 500 °C + / - 20 °C. This also improves the lattice structure of the alloy, but is significantly more time-efficient. Another advantageous development of inductive heating is the local limitation of the heat zone.

[0022] Another advantage is that the nickel-titanium alloy can be work-hardened to 21% to 40%, especially 35%, before processing the strand. If the material is work-hardened, the temperature range for heat treatment may shift. In this case, 30% work-hardening results in a heat treatment temperature that is approximately 100°C higher.

[0023] Furthermore, the nickel-titanium alloy is advantageously quenched following the tempering, in particular using water maintained at room temperature. In particular, immediately after heat treatment or tempering, i.e., for example, after removal from the furnace, the processed nickel-titanium alloy is brought into contact with a medium maintained at approximately 20 to 25 °C, such as water, in particular. This quenches the nickel-titanium alloy, altering its lattice structure in such a way that, in addition to its bendability, its mechanical stability with regard to the elongation of the working area is also improved.

[0024] Preferably, the working area is connected to the shaft by pressing, welding, or injection molding. The first two methods are particularly suitable when the shaft is made of a metallic material. Direct injection molding of the shaft onto the working area, i.e., onto the first end of the working area, is particularly preferred when the shaft is made of an injection-moldable plastic material. For example, an injection molding technique is used in this case.

[0025] Furthermore, the invention also describes the use of a nickel-titanium alloy which essentially consists of 38 to 46 at% nickel, 46 to 53 at% titanium, 5.5 to 8.8 at% copper, and 0.05 to 0.15 at% chromium, wherein the chromium content is in particular 0.08 to 0.13 at% and furthermore in particular 0.01 at%. The use provides that the nickel-titanium alloy is used to manufacture a root canal instrument, whereby the root canal instrument is characterized by a particularly flexible and bendable working area. The embodiments and advantageous developments of the root canal instrument according to the invention also apply to the inventive use.

[0026] The invention is described below using an exemplary embodiment in conjunction with the drawing. In the drawing: Fig. 1 a schematic side view of a root canal instrument according to an embodiment of the invention.

[0027] In detail, Figure 1 a root canal instrument 1 with a shaft 2 and a working area 4 connected to the shaft 2 by a connecting area 3. At a distal end of the shaft 2 there is a connecting piece 5. The connecting piece 5 serves for connection to a drive or a handpiece with which a dentist can operate the root canal instrument 1.

[0028] The working area 4 is to be regarded as a cutting area with which dead or bacterially infected pulp tissue from a root canal can be removed. The working area 4 has a first end 6 and a second end 7. The first end 6 is connected to the shaft 2 in the connecting area 3, while the second end 7 is exposed and has a tip. Overall, the course of the working area 2 from the first end 6 to the second end 7 is more or less conical, with the working area 2 comprising several areas in the axial direction XX which are provided with different helix angles, with the helix angles decreasing from the first end 6 to the second end 7.

[0029] Working area 4 consists of a nickel-titanium alloy containing 38 to 46 at% nickel, 46 to 53 at% titanium, 5.5 to 8.8 at% copper, and 0.05 to 0.15 at% chromium. Furthermore, the nickel-titanium alloy can contain a maximum of 500 ppm oxygen and nitrogen, a maximum of 500 ppm carbon, and a maximum of 50 ppm hydrogen. Due to the use of the nickel-titanium alloy, working area 4 is characterized by particularly good bending properties and high extensibility. This allows the working area to penetrate even hard-to-reach root canals to remove tissue remnants and form a conical root canal.Due to the high bending and extensibility of the working area 4, a diameter of the working area 4 can be made very small, since the working area 4 is nevertheless characterized by a high mechanical stability due to the use of the nickel-titanium alloy, such that breakage of the working area does not occur.

[0030] Preferably, the nickel-titanium alloy is tempered in a temperature range of 350 to 450 °C and quenched with water to room temperature (about 20 to 25 °C), which can improve the ductility and bendability while maintaining high fracture strength. Examples

[0031] Working areas for a root canal instrument were manufactured from the alloys listed in Table 1, as shown in Figure 1 shown, can be trained.

[0032] For this purpose, material strands were produced from the specified alloys and initially stored at room temperature (20 to 25 °C). The material was not work-hardened. The material strands were then stored in a furnace at 350 to 450 °C for a period of 30 minutes (the period can be between 5 and 60 minutes and preferably between 20 and 40 minutes). Heating in the furnace took place without undergoing a temperature ramp. The heat-treated working areas were then quenched in room-temperature water. Working areas for a root canal instrument were machined from the resulting alloy material. Table 1 further lists the physical and mechanical properties of the alloys used. Table 1 Example 1 Comparison example 1 nickel 42.50 at% 50.10 at% titanium 49.90 at% 49.90 at% copper 7.50 at% - chrome 0.10 at% - Oxygen and nitrogen Max. 500 ppm 220 ppm carbon Max. 500 ppm 320 ppm hydrogen Max. 50 ppm 50 ppm Stretching At least 30% 10% Tensile stress At least 800 MPa 1100 MPa Melting point 1310 °C - Young's modulus (austenite) 25-35 GPa (60-80 GPa) -

[0033] The strength and elongation were determined according to ASTM F 2516 edition 2018. To determine the maximum tensile stress (σ z ) the following formula was used: σ z = F / S (F = force in MPa, S = cross-sectional area in mm 2 ).

[0034] The force (F) was determined on a tensile and compression testing machine under the following parameters: Crosshead speed = 1 mm / min. Reference diameter (material) = 1.0 mm and 1.2 mm.

[0035] The modulus of elasticity was determined using the tensile test as the gradient until the material yields (beginning of plastic deformation according to Hooke's line).

[0036] As can be seen from Table 1, the alloy from Example 1 is characterized by particularly high elongation and tensile stress, resulting in high bending and elongation properties. Thus, a working area for a root canal instrument formed from the alloy from Example 1 is also characterized by particularly high flexibility. List of reference symbols

[0037] 1Root canal instrument 2Shaft 3Connection area 4Working area 5Connection piece 6First end 7Second end

Claims

1. A root canal instrument comprising a shaft (2) and a working portion (4) attached to the shaft (2), wherein the working portion (4) is made of a nickel-titanium alloy consisting of 38 to 46 At% nickel, 46 to 53 At% titanium, 5.5 to 8.8 At% copper and 0.05 to 0.15 At% chromium.

2. The root canal instrument according to claim 1, wherein the nickel-titanium alloy consists of 40.5 to 43.1 At% nickel, 48.7 to 50.8 At% titanium, 6.3 to 8.4 At% copper and 0.08 to 0.13 At% chromium and in particular 42.50 At% nickel, 49.90 At% titanium, 7.50 At% copper and 0.10 At% chromium and / or wherein the nickel-titanium alloy according to ASTM F 2063-15 comprises a maximum of 500 ppm oxygen and nitrogen and / or a maximum of 500 ppm carbon and / or a maximum of 50 ppm hydrogen.

3. The root canal instrument according to one of the preceding claims, wherein the nickel-titanium alloy has been cold worked by 21 to 40%, in particular by 35%.

4. A method for manufacturing a root canal instrument (1) according to one of the preceding claims, comprising the steps: - providing a nickel-titanium alloy that is made of 38 to 46 At% nickel, 46 to 53 At% titanium, 5.5 to 8.8 At% copper and 0.05 to 0.15 At% chromium, in the form of a strand, - machining the strand to form a working portion (4) and - connecting the working portion to a shaft (2), wherein the connection of the working portion (4) to the shaft (2) is carried out in particular by pressing, welding or injection molding.

5. The method according to claim 4, comprising a step of tempering the nickel-titanium alloy in a temperature range of 350 to 450°C or comprising a step of heat-treating the nickel-titanium alloy by means of induction for 1 second to 60 seconds at a temperature of 500°C +-20°C.

6. The method according to claim 4 or 5, wherein the nickel-titanium alloy is cold worked to 21 to 40%, in particular to 35%, prior to machining the strand.

7. The method according to claim 5 or 6, comprising a step of quenching the heat-treated or tempered nickel-titanium alloy to room temperature, in particular using water.

8. A use of a nickel-titanium alloy made of 38 to 46 At% nickel, 46 to 53 At% titanium, 5.5 to 8.8 At% copper and 0.05 to 0.15 At% chromium for manufacturing a root canal instrument (1).